Fixture for making honeycomb panel



July 1960 H. R. HERMAN ETAL 2,944,504

FIXTURE FOR MAKING HONEYCOMB PANEL 6 Sheets-Sheet 1 Filed NOV. 26, 1954AJJi oBRooK July 12, 1960 H, R, HE MAN m; 2,944,504

FIXTURE FOR MAKING HONEYCOMB PANEL Filed Nov. 26, 1954 6 Sheets-Sheet 2INVENTORJ'. 1.12. HERMAN E-AZALJOEROOK Cf fk r/ F 7-- mf July 12,- 1960H. RQHERMAN ETAL 2,944,504

FIXTURE FOR MAKING HONEYCOMB PANEL 6 Sheets-Sheet 3 Filed Nov. 26,

a K /u my NM ER w VEJ m J RA 2 w J w wh July 12, 1960 H. R. HERMAN ETAL2,944,504

FIXTURE FOR MAKING HONEYCOMB PANEL Filed Nov. 26. 1954 6 Sheets-Sheet 4IN V EN TOR. I]. I2. HERMAN BY B.R.AL.SOBRO0K ATTORNEY July 12, 1960 H.R. HERMAN ETA!- 2,944,504

FIXTURE FOR MAKING HONEYCOMB PANEL Filed Nov. 26. 1954 6 Sheets-Sheet 5"fnmmmn $1 filv iilfllllllffl l I l T f I g i gmumm lifl gmumlm W mmINVENTORS.

ER.H'RMAN 5.12. ALSOBROOK ATTORNEY y 1960 H. R. HERMAN ETAL 2,944,504

FIXTURE FOR MAKING HONEYCOMB PANEL Filed Nov. 26. 1954 6 Sheets-Sheet 6I: Ill

INVENTORS. 7 z 9-. .Z Z ACRJYERMAN BY aausozeomwar/11M JOI/JPCE I 9%ATTORNEY United States Patent 2,944,504 FIXTURE FOR MAKING HONEYCOMBPANEL Hartley R. Herman, La Mesa, and Benjamin R. Also brook, ChulaVista, Califi, assignors-to Rohr Aircraft Corporation, 'Chula Vista,Califl, a corporatxonof Cali! fornia y Filed Nov. 26, 1954, Ser. No.471,394

This invention relates to a panel structure of sandwich type in whichthin metal shaped somewhat like a honeycomb is secured between twoenclosing skins and to the apparatus and method used forfabricating suchpanel.

An object of the invention is to provide a fixture for holding thesandwich structure; while its components are distortion. I d In Anotherobject is to provide a holding fixture made up of a number: of smallindividnalcomponents soconnected together that it will remain rigidandhold its-contour evenwhen repeatedly heated to a-te mpe rature of about22005 F. :1. I a

A further b eet is ts provide such a nnate avin a e genefal forni'of theusual cardboard partition' hsed to pack eggs in egg crates, and toprovide. for the free c1rculation of gas through the individual "stripsmaking'up, the lattice work so that thesandwich may beheatedsubstantially uniformly throughout;

Another-object is 'to .providesuch, a lattice structure which, whilemaintaining the necessary rigidity, is yet of small mass andheatcapacity so that it requires only asmall amount of heat to besupplied toit to raise its temperature to that required for brazing the sandwichcomponents together; a k e -Anoth'er object is to provide means forstiffening the lattice structure and preventing one portion of it from.shifting with reference to other portions 1n padditloni'to therigidityflprovidedlby the contact of the lattice strips with eachother.'', This additional stiffening means is prefwich are placed, thefurnace being heated by a suitable heating means to a temperature abovethe brazing telnperature.

Another object is to provide such a mufile which will distribute theheat received from the source of furnace heat and prevent the heat raysfrom such source from directly impinging on the sandwich and therebycausing uneven heating thereof.

A further object is to provide for the slow, uniform cooling of thebrazed sandwich by removing the muflle from the furnace and permittingthe sandwich to remain in the'muffle while cooling. This procedureprevents the cool ambient air from reaching the sandwich with resultantuneven cooling thereof.

4 Anotherobject is to provide means for supporting the mufile out ofcontact with the furnace to permit free circulation of the furnace gasesaround the muffle thereby being brazed together which is capable ofheating and cooling with the sandwich with a minimum. amount of thesandwich...

embodying-the invention; I

I Further objects will become apparent as the description proceeds; Fora better understanding ofthe invention reference is made to theaccompanying drawingsf in I jFi'g. lfisa perspective view of ahoneycombsandwich Fig. 1A is a detail view of a portion of theho'neyooir'nbi =Fi'g. 2 isa perspective view of a holding fixturecontaining the sandwich of Big. 1;

I Figs; 3 and 4 are views of latticestrips usedinthe fixture of Fig. 2;

e'rablyv perforated to permit the free how of gas there-K through forsecuring a more uniform heating.

.- A further object is to provide for a small amount of I slippage ofthe sandwich with reference to the fixture by means of a thin sheetinterposed between them, thereby preventing ,warpage and change in thesandwich contour as I it cools after brazing. V

Another object, is to provide means between the supportinglattice andsandwich to prevent the concentration of-pressure in narrow areas of thesandwich and assure admore uniform pressure distribution over thesandwich y j brazed to a covermgskm 17 and theirnnner ends brazed to aconcave shaped skin 18, the skin 18, terminating in before and duringthe brazing. t r

In cases where the sandwich has a convex contour, a further objectis toprovide a thin metal sheet enveloping the sandwich and arranged to applysubstantiallyuniform Fig. 5 is a view partly in section and partlydiagram matic of a honeycomb sandwich and muflle in afurnacei Fig. 6 isa top view of a holding fixture illustratinga' modified form of theinvention; I

Fig. 7 is an end view of the fixture of Fig. 6;

i V .Fig. 8 is a detail of Fig. 6;

-Fig. 9 is a sectional view on line 9 9 of Fig. 6 also showing ahoneycomb panel in the fixture;

. ,Fig. 10 is a perspective view of the sandwich panel shown in Fig. 9;j W

v Fig. 11 is a perspective view showing a holding fixture containing asandwich panel and; I I ,7

Fig. 12 is a sectional view on line 12-12 of Fig. 11. Referring to Figs.1 and 2 the invention is illustratedin connection with the constructionof, a honeycomb sandwich 15 having a central core composed of diamondpressure to the various portions thereof, thethickness and material .ofthe sheet preferably being such that the sheet t A still further objectis to provide forthepreheating of .the' sandwich assembly prior tobrazing in amuflle not muchllarger than it to a temperature somewhatbelow the Brazing temperature and to complete the brazing ina 7 'high'temperature furnace' in which 'the muflle andfsand shaped cells 16 whichare connected together by weldingor other knownmeans, the outer ends ofthe cells being straight edges 19 to which are brazed the ends of a pairof inwardly curved flanges 20, 21. The lower ends 22 of skin 17 arealsostraight and have brazed thereto outwardly curved flanges 23, 24 of theshape shown. All of the above parts are preferably made of stainlesssteel which has high tensile strength and although the thickness of themetal composing the honeycomb cells may be only from 1 to 3 thousandthsof an inch, nevertheless when the parts of the sandwich are brazedtogether the resulting structure has great strength and; stronglyresists torsion and bending. Prior to brazing, in a manner 'to belaterdescribed, the flanges 20, 21 arettack welded at 'spaced apart points toedges 19 and. flanges 23, 24

similarly secured to the edges 22 of skin 17 -As shown Patented July 12,1960 V in Fig. 1A, the honeycomb is preferably provided with small holesthrough the metal thereby providing passages through which gas may passfrom one cell to another. The holes 25 thus assure that the pressurewithin all the cells is substantially the same.

The brazing together of the aforementioned parts is done in a fixture 26of the type shown in Fig. 2, which comprises a horizontal base 27 in theform of a lattice composed of a plurality of longitudinal strips 28interlocked with a plurality of transverse strips 29. Each strip 28 hasa series of equally spaced apart slots 30 and a set of holes 31therethrough and eachstrip 23 has a series of equally spaced apart slots32 and a set of holes 33 therethrough, as shown in Figs. 3 and 4. Byassembling the strips together so that the unslotted portion of eachlongitudinal strip 28 fits into the slots of the transverse strips 29,in a manner similar to the cardboard partitions used to pack eggs in eggcrates, a rigid lattice 27 is provided which contains a relatively smallamount of metal, is light in weight and may easily be assembled andtaken apart. For certain purposes it is desirable to further stiffen thelattice by securing its component strips together at their points ofintersection by welding or other means (not shown). If the top of thelattice is not plane within the desired tolerance, it

may be made flat within a tolerance of .001 inch by.

grinding. The top face of the lattice serves as a horizontal referenceor datum plane of the fixture. The strips 28 and 29 are preferablycomposed of a steel alloy capable of standing high temperatures withoutappreciable distortion and may be about .062 inch thick when'the stripscomposing the lattice are 1 inch apart. The holes 31, 33 permit hot gasto circulate through the lattice structure promoting its more rapidheating and more uniform temperature. Attached to the bottom of thelattice are a set of angle irons 34, the center only of each angle beingpreferably welded to the lattice.- These angles support the latticewhile the fixture is heated as described below and permit the lattice tofreely expand and contract unrestrained by the angles which may expandat a different rate than the lattice so that buckling of the latticewould result if it were secured to both ends of the angles. The freespace between the angles and lattice permits the free circulation of hotgases therethrough to assist in the rapid heating of the fixture and amore uniform temperature distribution.

A plurality of similar formers 35 have flat edges seated on lattice 27,each former preferably being composed of a plurality of annular segmentssecured together by bolts 37, as shown. Deep slots 38 are cut in theperiphery of each former and longitudinally extending thin strips 39 areseated in these slots so that the several formers are in alignment andparallel to each other. Each former is secured in place to lattice 27 bybolts 4-0 which pass through a pair of angle irons 41 which are Weldedor otherwise secured to lattice 27. Near its base each former terminatesin a vertical edge 42, against which rests the vertical edge of formerextension 43 whose upper end 44 engages the end of the honeycombsandwich and whose curved edges 45, 46 fit'against flanges 20, 24respectively and flanges 21, 23. After" assembling the formers 35 andlattice strips 39, if their outer edges do not exactly conform to thedesired shape, the outside periphery of the assemblyis ground orotherwise machined to shape.

Before assembling the sandwich components shown in Fig. 1, the insideface of skin 17 and outer face of skin 18 are covered with brazingmaterial as are also the edges 19 and 22 of the four channel members.The brazing material may be of any known type which is compatible withthe metals to be brazed together and, in the illustrated example, may bea thin coating of acrylic resin applied by a spray gun. The metalbrazing alloy may then be applied as a thin sheet or as a fine powderdusted or sprayed onto the resin coating. Before placing the 4 assembledprepared sandwich in the brazing fixture, a stainless steel sheet 50having a thickness of about .020" is laid on the curved periphery of thefixture to cover all the formers and strips 39 and the assembledsandwich then placed in position, as shown in Fig. 2. The formerextensions 4-3 are then put in place and an enveloping sheet 51 ofstainless steel draped over the sandwich and the flanges 23, 24. Sheet51 preferably'is between .030 and .040" thick and made of stainlesssteel. Elongated clamp jaws 52 are pressed against the lower ends ofsheet 51 by means of a series of bolts orscrews 53 threaded in spacedapart similar supports 54. The face of jaw 52 which presses againstsheet 51 is serrated or otherwise roughened to give a better grip and iscontoured to the shape of flange 24. Each support 54 is attached tolattice base 27 preferably by a bolt (not shown) which passes throughthe lattice and enters a threaded hole in the bottom of the support. Allthe supports together with their adjusting screws are thus readilyremoved from the lattice. Supports 54 may be made of Invar alloy andscrews 53 of metal which has a substantially higher coeflicient ofexpansion than Invar so that as the temperature increases during thebrazing, the screws exert a somewhat greater pressure on jaws 52 whichin turn keep enveloping sheet 51 tightlypressed against the outer skin17 of the sandwichnotwithstanding the increase in length,

on the floor 56 ofthe mufile. A stream of argongas is then passed intothe muffie to purge itof air and a stream of hydrogen gas then passedinto it until the mutlle and honeycomb are completely filled withhydrogen. The sandwich and muffle are then preheated by any suitableheating means to a temperature of about 500 F., the heater illustratedconsisting of two Calrod electric heaters 57 supplied with current fromthe usual A.C. source (not shown). r It will be understood that morethan two heaters may be used, if desired. This heating partly purges themuffle and assures the removal of all moisture therefrom.

After preheating in the muflie, the mu-flle and sandwich are placed in ahigh temperature furnace 58, the muffle spaces 61through which thefurnace gases may circulate to accomplish more uniform heating. Thefurnace walls are preferably lined with fire brick (not shown), in aknown manner. The furnace'may be heated by a plurality of electricheaters 62 diagrammatically shown or by hot combustion gases suppliedfrom a burner (not shown), the temperature in the furnace beingmaintained from to 200 F. above the melting point of the brazingalloy.An inert gas as, for example, hydrogen which will not'oxidize orotherwise form compounds with the metal of sandwich 15 is introducedinto a metal heating coil 63 in the furnace, the outlet of the coildischarging the hot gas against a baffle 64 in the muflie, the bafliehaving discharge outlets 65 which serve to direct the hot inert gasalong the wall of the muffle and thus prevent it from impinging directlyonthe sandwich with resultant uneven heating thereof. V

As soon as the furnace door (not shown) is closed, the inert gas ispassed through coil 63 to heat it, the

gas leaving through a pipe 66. Soon after the sandwich of which thecurved end of bar "68 abutts.

supply into the muffle against baffle 64, the hydrogen being supplieduntil the sandwich cools down to about 800 F., and serving to presentoxidation of the sandwich. The hydrogen supply is then stopped and argon:supplied instead, argon being admitted to the mu-fiie until it hasreached normal room temperature. The argon supply is then shut off andthe cooled fixture and sandwich removed from themufile.

While one muifle is cooling, another preheated one with its containedsandwich may be placed in the furnace and the'brazing eifected in themanner described. The furnace is thus fully utilized audit is notnecessary to fill it with inert gas while the brazing is elfected. Alsoa further saving in this gas is secured by making the motile onlyslightly larger than fixture 26.

Figures 6 'to 9 show a lattice fixture 66 adapted to support the severalparts of the'sandwich panel 67 shown .in Fig. 10 during brazing. Thispanel comprises core cells 16 of the type previously described, an uppermetal sheet or skin 17 which is to be brazed to the upper end of thecells and a lower sheet 18 to be brazed to their lower end, the planesthrough the. ends of the cells tapering toward a. tapered bar 68 whichis recessed to provide faces 69 to whichthe ends of sheets 17, 18 arebrazed. The end of the cell core opposite bar 68 is brazed to thevertical web 70 of a channel 71 whose outwardly extending legs 72 arebrazed to a pair of elongated doublers 73 which also overlie the cellcore and are brazed thereto and also to the sheets 17, 18. Brazed to theends of sheets 17,

18 and extending past the ends of the cell core are four' strips 74which serve to distribute any applied load over a larger area of thecell core, the ends of these strips also being brazed to bar 68.

Fixture 66 is a lattice having longitudinal strips 28 and transversestrips 29 which are interlocked in the manner above described, thefixture having an upper section 75 whose lower surface is ground fiatpreferably within a tolerance of .001 inch anda lower section 76 whoseupper face is ground flat within the same tolerance. section 76 has apair of angles 34 attached/to it in the manner above described forsupporting the fixture in a mufile. Attached to the rear side of section76 by bolts 77 is an angle iron 78 in which are seated the ends of threealigned locating pins 79 against the upper ends Secured in angle 78 area plurality of cylindrical guide pins 80 which enter holes 81 in anangle 82 secured 'to' upper fixture section 75 by blots. 83. Pins 80have narrow slots 84 to receive wedges 85 At the opposite end of thefixture similar angles 82, 78 are provided but instead of the locatingpins 79 locating blocks 86 of the shape shown'in Figs. 8 and 9 are used,each block having a hole 87 through which guide pin 80 passes. Theseguide pins also pass through holes in two thin metal'sheets, the uppersheet 88 extending over the'top of the sandwich and the lower sheet 89over its entire bottom face. The sheets 88, 89 function to distributethe pressure in the same manner as above described in connection withthe sheet 50. The uncovered ends 90 (see Fig. 10) of the honeycomb coreare restrained by rest-raining blocks 91 held in place by pins 92 Whoselower ends are attached to bottom fixture'section 76 by welding or othermeans (not shown).

To weld the component parts of the sandwich together, the surfaces to bewelded are treated as above described in connection with Fig. 2, sheet89 placed on lower section 76 and the other parts positioned as shown inFigs,

6, 7 and 9. If the weight of upper fixture section 75 providessufiicient pressure to hold the parts to be brazed Lower vention inwhich vacuumand gas pressure are utilized to apply pressure toa'sandwich structure to hold the skins 17 and 18 in contact with theends of cells 16. The upper section 93 of the fixture has intersectinglattice strips 94 of the type above described, the lower edges of whichrest on a perforated plate 95 whose lowerface is ground to the contourof the desired sandwich 96, Plate' 95 rests on the upper skin 17 whichis to be brazed to the upper end of cells 16. The skin 18 to be brazedto the lower end of the cells rests on perforated plate 97 whose topface is ground to the curved contour of sandwich 96. The bottom section98 of the fixture is airtight and may be connected to a vacuum pump 99by a valve 100; Bottom section 98 has attachedthereto a vertical plate101 (Fig. 11) which carries a channel 102 in which is disposed acontinuous mass of sealant material 103. Upper fixture section 93 hashermetically secured thereto a rectangular hollow casing 104- havingvertical side and end walls 105 which extend into the sealant 103. Uppersection 93 is guided by a set of vertical pins 106 whose lower ends aresecured to brackets 107 which in turn are attached to the sidewall offixture section 98. Wall 105 has attached to it a set of plates 108drilled to receive and slide along the pins 106, the latter beingslotted to receive the wedges 109. Surrounding the pins 106 are sleeves110 whose length is such that they take the weight of the fixturesection 93 and prevent its weight from hearing on sandwich 96. A pair ofZ shaped bars 111 extend along the entire side edges of core 16 and arebrazed thereto, the webs of these bars being pressed against the core bya plurality of screws 112 spaced about 6 inchesapart. The screws 112 arethreaded into supports 113 which are attached to the sides of plate 97by bolts 114. The sides of the panel are thus maintained to the requireddimensions.

The brazing material having been'appliedto the top sheet 18 and bottomof sheet 17 and to those faces of taneously dry hydrogen gas underpressure is conducted into hollow casing 104 by a pipe 115 leading froma tank 116 of dry hydrogen gas. This gas reaches the top face of skin 17and presses the skin firmly against 'core16 and causes the core toconform to the contour of its bottom skin 18'so that the entire panelhas the de- "sired size and contour prior to reaching the brazingtemperature in the furnace and during the brazing. When the brazing is'complete, the fixture and panel are re moved from the furnace and thevacuum maintained under sheet 18 and the hydrogen pressure over sheet 17until the parts have cooled to about 800 F. when the entire fixture ispurged with argon gas and the brazed panel removed therefrom.

In each of the illustrated examples, in order to'prevent the accidentalbrazing of the fixture tothe honeycomb panel, those parts of the fixturewhich contact the panel are covered with a thin coating of chromiumoxide or aluminum oxide (A1 0 may be plated with chromium in a knownmanner and the plated fixture then heated in an oxidizing atmosphere toconvert the plating to chromium oxide.

This invention may be embodied in otherforrns or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present' embodiment of the invention is therefore to beconsid-' ered as in all respects illustrative and not restrictive, thescope of the invention being indicated by the appended claims, and allchanges which come within the meaning The entire fixture V an range aequivalency o th c aim a e intended t beemb f'r aced therein;

;H avii1 g us described th i ten io W a we lai as new and useful anddesire Qtoseeure by Letters ,Patent;is:

7,1 ,A lattice ,fixture adapted to support a honeycomb sandwich composedof a thinuyalled flexible cellular core, a;first thin skin in contact.With ,the lower end of said core and a second thinskin .in contact withQ-the upper end otsaid core while theskins are brazedto the core, saidfixture comprising ,a first set of separate parallel thin metal strips;arsecondset of separate parallel thin metal .strips interlocked witht-he;str'ipsof the first set, the top edges of all said Istripsbeing}machined to provide a supporting surface having the desired contour .ofthe brazed g sandwich, isaid tto'p edges of ,said ..strips extending.egenly spaced in 170th directions 1 whereby said supporting surfaceprovides a uniform support [for said thin-walled cellular core; and aseparable metal sheet in contact With-the topedges of said stripsand thelower face of said-first skin, the material and thickness of said metal,sheetvbeing selected-to .preventi the concentration of uptwardtpressureon -said first skin to regions thereof directly opposite the top edgesofsaidstrips in response to the applicatiomofpressure on thetopfaceofsaid .secblldiskill.

;2. .A-rfiXlZUIC adapted to hold upper and lower thin :skins to .theitopand bottom faces of the thin-walled :fiexible cellular core of asandwich; said fixture compris- .ing:,a-lowerlattice-having an upperface shaped to the idesiredi, contour of the sandwich; an upperlatticehaving a; lower face shapedtothe contour ofthe desired sandtwichsaidrupper and lower faces eachcomprising even- 11y spaced thin edgesextending innboth directions toprovide uniform supporting surfaces forsaid thin skins and the top andbottom faces of saidthin-Walled cellularcore; a pairmf separabletthin flexiblernetal sheets interposedrespectivelyibetween said skins and said supportingsurfaces;i.andtguidemeans secured to the lower lattice arranged to guide. said upper latticetoward the 1 lowerlattice, the iweight of said upper lattice serving todeform said'sandwichstou-the contour of the upperaface of said lowerlattice.

3.A lattice-"fixtureadapedtov press upperand lowervideasupportingsurfaceshaving a contour. of predetermembers againstopposite ends 'of thefcoreji sai 8 mines ha e a aa fi rat i i aqr ithin-Walled core'iand ir'nen'tb'ersfa sepafa 1e flexible Irietal 't incontact with but" unconfiected to nie roy'eg e said sets ofstripasaidlower nieriibeiuesting on said flexible sheet and means engaging hemember for applying downward pressu're thfereto' g the'lirai- Ing- ."li"I L 4. A fixture adapted to hold upper and lower thin metal skins tothetop and bottom 'fac es of ajthin' wall'e'd cellular core and also tohold structural riiembersagainst opposite ends of saidpore; saidfixtureco a separable thin metal sheet in contactfwith y f: H of theupper skin butunattached thereto; means g above said sheet forapplyingdownwardpressure hereto; a second separable thin n etaljshe'etin conta the bottom face of said "lowerjskinlb'utunattached t reto; alattice having'a plurality of spac faces extending eyenly spa ed in b6 4contact with thebottomiaeejof sa and means carriedb'y said lattice,ranged to press said structural in s :ag edges of the core. 5. A fixtureadapted to hold upper and lower rnetal skins against thetop'and, walledhoneycomb core andalso'jto. h old'ltwo i'strue ral comprising: aseparable thin rnetal sheetfin contact the bottom face ofssaid lowerskin but unattaehed".,thereto; a supporting latticehaving'aplii'ralitfof spaced apart narrow faces extending'eyenly' spaeedin both directions and incqntact with the'bottorn}iaee ;of,said

rnetal sheet; a plurality offwidely spaced apartiloc ating pins carriedby said lattice and in contact ,wnnrnepen ipheraledge of one of saidstructural,inembers'j 'means carried by said lattice ande ngaging.theperiplieralgedge of the otherstructural menrber at a. plurality ofspaced regions thereof; and means associated w ithsa'i d latftiee forapplyi g d wnwar pressur 1: sai 1 11125619,

, References Cited in the file of thispatent TE ST TE PATENT

